Malte,
For this answer, I am assuming that the tcl datasource will remain the same and you will just ad_return_template the corresponding adp.
You might be able to take advantage of the content repository. One way would be to create a template content_folder for each subsite. Permissions could easily be controlled that way.
Of course, you still need to process the templates when serving pages. So the next step would be to register another filesystem storage area such as /web/sitename/templates/ with a directory for each subsite.
A third option would be to store the revisions in the standard CR storage, either database or generic filesystem storage, then publish them to the correct templates folder when they change. The tcl api to publishing content to the fileystem in the content repository should work for this.
This question comes back to the more general question of how to modify the built in adp templates provided by a package. I eventually want to genealize a prodedure like this to allow replacement of any adp template.
